diff --git a/Variant-USART.md b/Variant-USART.md
index a251e2a..1a0d096 100644
--- a/Variant-USART.md
+++ b/Variant-USART.md
@@ -12,6 +12,7 @@ You can adjust USART2_BAUD or USART3_BAUD parameters if you need different baud
 
 ## Wiring:
 * Connect blue wire to RX, green wire to TX and black wire to GND of Arduino on right sensor cable(shorter)
+* Only USART3(right sensor cable) is 5v tolerant
 
 ⚠ Red wire from sensor cable delivers 15v !!!